My S2 has been running well but on two occasions recently it has started misfiring and I don't know where to look.

Symptoms just started suddenly. Once when cold, once when hot and stopped in traffic. Seems to be worse or has greater effect at low revs as car cuts out but is present right through the range. It starts fine. Acceleration not great, steady dri ing bad. I tried driving home 10 miles and the tunnel area got very very hot. Smoke started to seep in to the cabin around the console. I think that must be exhaust. Plugs are all identical but sooty black. BPR6. Water gauge steady and in middle.

I'm hoping there might be ideas on here to help me please.

 

If you're running too rich, you can send a lot of fuel down to the cats, making them even hotter. This might explain some of the heat that you're feeling from the tunnel.

Given the running problems you're experiencing, have you checked your fuel system? How's your pressure, and does your regulator or damper show any signs of fuel in the vacuum line?

Cheers

 

So you think fuel, I originally thought too but with the misfire went possibly electric. I'll check the lines.

 

Often this is a blown FPR or damper leaking fuel into the vacuum line.
It could also be a bad DME temp sensor fooling the DME into skewing very rich.
Also worth looking to see if the underbody flocking is scorched around the cat converter, clear indication the converter is getting superheated. Which is bad.

 

Hmm. Sounds like a path but definitely superheated cat. Smoke from that area for at least 30mins after switch off.

Question in my head is why intermittent. Ran well between two instances.

 

I’m going through the same thing and it was def leaking fuel from dampener into vac line. Be careful driving around like that because I was close to leaving the vac line off to see if that was the problem and then I noticed fuel coming from the top of dampener. Get a fire extinguisher too. There’s a company that makes the dampener for like 120. I’ll try to post a link for everyone

 

So checked the Damper and the Regulator vacuum lines and both dry as a bone. Have to try and measure pressure somehow also as the cat area was very hot. What gets me is it was present the first time when the car was cold so I doubt it's the dme temperature sensor as the car was genuinely cold and hadn't been used in a week. Could crank sensor cause rich running and stuttering.

 

To observe a problem with the DME temp sensor you'd have to measure it when it's acting up. I had one go bad on an 84 Mustang and it was intermittently causing massive rich fueling.
You might have another issue, but I have experienced a blown FPR, damper and bad temp sensor all causing rich running so that's my direct experience.

*edit* there is an AFM temp sensor and AFM wiper track issues that could also be a factor

 

Could be a bad injector or maybe a bad signal going to it. Since these injectors are batch fired if one or two hang open that will give you a rich condition.

 

Don't overlook a clogged/collapsed catalytic converter.

 

I would check the AFM - I had a similar issue and the pickups needed to be re-positioned. Stuttering and cutting out at certain parts of the throttle range.
http://www.clarks-garage.com/shop-manual/elect-22.htm

Recommend reading through the Clarks Garage troubleshooting guide/testing methodology, all of the previous mentioned suggestions are shots in the dark and will lead you nowhere or cause you to replace parts that dont need to be replaced. Walk through the testing process step by step and do this methodically and in order.
https://www.clarks-garage.com/shop-manual/ts-01.htm